Turbocharger (Ex: Greddy)
With a compressor design very similar in appearance to a centrifugal supercharger, a turbocharger could easily be mistaken at first for its pulley driven brother. The big difference is, turbochargers are driven by exhaust gases, not by belts and pulleys. Flip over a turbocharger and you'll see the cast turbo inlet and outlet, along with a wheel referred to as the turbine. From the exhaust ports, gases flow into exhaust manifolds that feed the turbocharger's inlet. As the gases flow from the inlet to the outlet port, they spin the turbine wheel as they rush through the turbo's hot side. This turbine wheel is connected by a shaft to the compressor wheel, which can spin up to 100,000RPM, generating some serious boost. Turbochargers were the magic behind the early 1980's Formula One racing machines, which developed more than 1000HP out of 1.5L engines.
GReddy's turbo kit uses cast exhaust manifolds, twin TD05H-18G turbos, and external wastegates. The kit can be easily upgraded to make more than 600whp. |
Intercooling is always highly recommended when using boost. Both Vortech and GReddy use a front-mount air-to-air setup. |
With the turbos mounted low and close to the exhaust ports, the GReddy turbo kit almost flies stealth when viewed from above. |
In a supercharged and naturally aspirated car, exhaust gases are merely spit out the tailpipe, where in a turbo car, the otherwise wasted energy in the exhaust path is used to generate boost. Free of pulleys, belts and gears, turbochargers are much more efficient than superchargers, but much more complex as well.
To prevent too much boost from generating in the engine, turbo systems utilize a management system known as the wastegate. Internal and external wastegate designs exist and both accomplish the same task. A wastegate remains closed during initial use, using exhaust gases to increase pressure and build boost until the wastegate detects that the preset boost level has been reached. At that time, the wastegate opens to bleed off excess exhaust gases and continues to maintain the same boost level. With proper control of the wastegate, a turbo can be setup to generate boost as soon as it enters its boost threshold and can control boost to prevent an 80psi-induced detonation wave from smashing your engine to pieces.
The boost threshold, commonly and incorrectly referred to as "lag", is the RPM at which your engine generates enough exhaust flow to spin your turbo. Keeping the boost threshold low is the reason why stock WRX's use such tiny turbos, and big power with no regard for a low boost threshold is the reason why 1000whp Supra's regularly use snails the size of Texas.
Because the 350Z uses a "V" configuration six-cylinder engine, the most responsive turbo setup is to use two turbochargers and mount one on each side of the engine, using three cylinders to feed each turbo. GReddy's 350Z kit utilizes this twin-turbo design, and while the door to 600whp+ can be opened with this turbo system, installation and maintenance can be higher than that of a supercharger system. Already a tight engine bay, squeezing two exhaust manifolds, two external wastegates, two turbos, two intakes, intercooler piping and two downpipe elbows under the hood of a Z is not an easy task. On our own Projekt Z, the steering shaft and starter had to be temporarily removed in order to maneuver the turbos into place.
Also, because turbocharger systems reference their boost levels based on outside air conditions, care must be taken to ensure proper boost control under all driving conditions. Crawling through traffic on a sunny day and blasting along on a cold, rainy night are two completely different situations that can produce large differences in the amount of air a turbo machine ingests. The same precaution exists for taking a turbo car to different altitudes, making a good boost controller and proper engine tuning a must.
GReddy sells a well-designed electronic boost controller, a measure that can be taken against boost spikes and overboosting, allowing safer operation of a turbo system. A boost controller also has the ability to let an end user crank up the boost at the touch of a button, allowing nearly limitless power potential.